About CMT2C
How CMT2C works: the biology
At a glanceTRPV4 is a gate in the cell membrane that lets calcium in. In CMT2C the gate is overactive, and new mouse research suggests the damage may begin in the blood vessel lining that protects the spinal cord [15].
The plain-language version
1. TRPV4 is a sensor and a gate. TRPV4 is a channel in the cell membrane that lets positively charged particles, including calcium, into the cell [23]. It responds to moderate warmth, cell swelling and certain natural chemicals in the body [23]. It is found in many tissues, including nerve cells, the bladder, the lining of blood vessels, the kidney, the inner ear and skeletal muscle [23].
2. In CMT2C the gate is too active. The current consensus is that neuromuscular TRPV4 variants cause a gain of channel function, meaning the channel is more active than normal [6]. In the original discovery work, mutant channels produced marked cell toxicity and increased channel currents [10], and increased calcium channel activity was a shared property of the mutant proteins [14].
3. The brake comes off. The neuropathy mutations sit on the part of the protein’s surface where a regulatory partner called RhoA docks [25]. RhoA works like a brake that keeps the gate from opening too easily [25]. Neuropathy mutations almost completely block RhoA binding [24], and disturbing this docking site increases channel activity [25].
4. Too much calcium harms nerve cells. In a fruit fly model, a CMT2C mutation caused nerve cell dysfunction and degeneration of the axons (the long nerve fibers), and it disrupted the transport of mitochondria (the cell's power stations) along the axons before any degeneration was visible [26].
5. A surprise from mice: the blood vessels matter. In mice carrying patient mutations in their own Trpv4 gene, removing the mutant gene from the cells lining blood vessels rescued the mice from the disease, while removing it from nerve cells, their support cells (glia) or muscle did not [15]. Mice with symptoms had localized leaks in the barrier between the blood and the spinal cord, and lost motor neurons (the nerve cells that control muscles) in specific regions [15].
6. Blocking the channel helped, even after symptoms began. In these mice, a TRPV4-blocking drug stopped the barrier damage and largely reversed the disease in mice that already had symptoms [15]. A TRPV4 blocker also rescued the fly model [26]. This is the scientific basis for testing TRPV4 blockers in people [15].
What is still missing. These results come from flies, cells grown in the lab and mice. I found no human tissue or imaging evidence of barrier breakdown in people with CMT2C, and no second laboratory that has repeated the mouse finding in its own animal model.
For the science-minded
The channel
- TRPV4 is a calcium-permeable, non-selective cation channel of the TRP vanilloid family. Four subunits form the channel, each with six membrane-spanning segments and a cytoplasmic N-terminus containing an ankyrin repeat domain (ARD) [23].
- Activators include moderate heat, cell swelling, and endogenous lipids such as anandamide, arachidonic acid and its epoxyeicosatrienoic acid metabolites [23]. One review places the temperature activation range at around 27 to 34 °C [27].
- Cryo-EM structures of human TRPV4 in complex with RhoA exist in several functional states. Opening involves rotation of the intracellular ARD and of the S6 gate. A synthetic agonist (GSK1016790A) and an antagonist (GSK2798745) bind the same cavity with opposite effects [25].
Where the mutations sit, and nerve versus bone
- Neuromuscular variants cluster on the convex face of the ARD and target conserved arginine residues [6]. Skeletal dysplasia variants are spread through the gene, with hot spots at Pro799 and Arg594 [6].
- Neuropathy mutations (R232C, R237L, R269C, R315W) sit on the surface-exposed ARD face and nearly abolish RhoA binding, while skeletal dysplasia ARD mutations sit on the opposite face and variably preserve it [24].
- Variants that cause mixed nerve and bone disease are reported to produce severe gain of function [28].
- Why one gene causes nerve disease in some people and bone disease in others remains only partly explained. A 2013 review listed this among the open puzzles of TRPV4 [23].
For a variant-by-variant guide, including what “uncertain significance” means and how classifications change, see TRPV4 variants.
The gain-of-function debate
- Two of the three 2010 discovery papers reported gain of function [10]. The third reported reduced surface expression and reduced calcium responses, interpreted as loss of function [12].
- The same mutant (R269H) behaved as gain or loss of function in different laboratories, which suggests the result depends on the method and cell type [23].
- Later evidence supports gain of function: larger and faster calcium responses in neurons carrying R269C [26], gain of mutant channel activity in the native blood vessel lining cells of knock-in mice [15], and toxicity rescued by TRPV4 antagonists in models [26].
Downstream mechanisms
| Mechanism | Key evidence | Model | Source |
|---|---|---|---|
| Calcium overload through CaMKII | A genetic screen found CaMKII to be the most potent modifier; reducing it eased the disease features | Fruit fly | [26] |
| Stalled mitochondrial transport | Mutant TRPV4 disrupted transport in both directions before degeneration; a TRPV4 antagonist normalized it | Fruit fly larvae | [26] |
| RhoA released from TRPV4 | Mutations disrupt RhoA binding independently of channel activity; RhoA inhibition restored neurite length | Cells and fruit fly | [24] |
| Dominant effect within the channel | Mutant subunits suppress RhoA binding by normal subunits in the same channel | Cells | [24] |
| Barrier breakdown in blood vessel lining | Deleting the mutant gene from endothelial cells rescued mice; an antagonist reversed the barrier defects | Knock-in mice (R269C, R232C) | [15] |
| Barrier disruption across many mutations | Of 51 known disease mutations tested in lab-grown eye cells, 7 of 22 neuropathy mutations weakened the cell barrier, as did most metatropic dysplasia mutations and no other skeletal ones; an experimental inhibitor from the company developing ABS-0871 (ABS-0872, a different compound) prevented or reversed this for the few mutations tested | Cell models (industry study) | [29] |
Why the voice box, diaphragm and shoulders?
The clinical pattern is well documented, but its cause has not been established. In mice, motor neuron loss is regional and barrier disruption is focal [15]. A related grant abstract describes focal barrier breakdown “particularly in the ventral horn of the cervical spinal cord and brainstem” [30] (not peer reviewed). These areas supply the nerves to the muscles of the voice box, diaphragm and shoulders, so damage there is a plausible explanation for the human pattern. This remains a hypothesis and has not been shown in people.
General axon biology
- Axons have an active self-destruct program. Its key players are NMNAT2, a survival factor, and SARM1, a pro-degenerative enzyme that can be targeted by drugs [31].
- NMNAT2 makes NAD+, and SARM1 destroys NAD+ when it senses that the balance has shifted. Deleting or inhibiting SARM1 protects axons in several models [32].
- No evidence was found that SARM1 has been tested in TRPV4 models. On this site, SARM1 is general nerve biology, not a CMT2C finding.
What changed from 2024 to 2026
- The field shifted from a neuron-centered model toward a blood vessel and barrier model [15], supported by a separate 2025 cell study by an industry team [29].
- GeneReviews was updated in December 2025 [6], and the registry paper defined the bulbar, skeletal and proximal picture [3].
- A June 2026 preprint review called the endothelial mechanism “paradigm-shifting” and noted that no TRPV4 therapy has been approved [33] (not peer reviewed).